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Original author(s)Anthony Minessale
Developer(s)Different contributors
Stable release1.10.6 (March 25, 2021; 5 months ago (2021-03-25)[1]) [±]
Written inC
Operating systemLinux,[2] macOS,[3] Solaris,[4] FreeBSD,[5] NetBSD,[6] OpenBSD,[7] DragonFly BSD,[8] Windows[9]
Available inmulti-lingual
TypeVoIP software, Softswitch
LicenseMozilla Public License (MPL) Edit this on Wikidata

FreeSWITCH is a free and open-source application server for real-time communication, WebRTC, telecommunications, video and Voice over Internet Protocol (VoIP). Multiplatform, it runs on Linux, Windows, macOS and FreeBSD. It is used to build PBX systems, IVR services, videoconferencing with chat and screen sharing, wholesale least-cost routing, Session Border Controller (SBC) and embedded communication appliances. It has full support for encryption, ZRTP, DTLS, SIPS. It can act as a gateway between PSTN, SIP, WebRTC, and many other communication protocols. Its core library, libfreeswitch, can be embedded into other projects. It is licensed under the Mozilla Public License (MPL), a free software license.


The FreeSWITCH project was first announced in January 2006 at O'Reilly Media's ETEL Conference.[10] In June 2007, FreeSWITCH was selected by Truphone for use,[11] and in August 2007, Gaboogie announced that it selected FreeSWITCH as its conferencing platform.[12]

FreeSWITCH's first official 1.0.0 release (Phoenix) was on May 26, 2008.[13] A minor 1.0.1 patch release came out on July 24, 2008.[14] At ClueCon 2012 Anthony Minessale announced[15] the release of FreeSWITCH version 1.2.0[16] and that the FreeSWITCH development team had adopted separate stable (version 1.2) and development (version 1.3) branches.

FreeSWITCH 1.4, released at early 2014, is the first version support SIP over Websocket and WebRTC.

FreeSWITCH 1.6 added support for video transcoding and video conferencing, Verto protocol for WebRTC, and all WebRTC codecs and standards.

FreeSWITCH 1.8 was released at ClueCon in 2018 with further updates and stability improvements to the project.

SignalWire Inc was founded in 2018 to provide commercial cloud telecommunication services utilizing an elastic FreeSWITCH core, and provide a permanent commercial sponsor for the open source project that was controlled by the founders of FreeSWITCH. It then acquired FreeSWITCH Solutions.[17]


According to the lead designer, Anthony Minessale,[18] FreeSWITCH is intended to be a softswitch that is built on top of a solid core, driven by a state machine.[19] The stated goals of the project include stability, scalability, and abstraction.

To reduce complexity, FreeSWITCH uses freely available software libraries that perform needed functions. Some dependencies are:[20]

Not all of these software dependencies are required to build the core freeswitch application, but are dependencies of various external modules, such as codecs. FreeSWITCH is a modular application, in which modules can extend the functionality, but the abstraction layer prevents inter-module dependency. The goal is to ensure that one module is not required to load another.[21]


FreeSWITCH includes many modules that provide many telephony applications, such as conferencing, XML-RPC control of live calls, interactive voice response (IVR), speech synthesis and speech recognition, public switched telephone network (PSTN) interfaces for analogue and digital circuits, voice over IP protocols including Session Initiation Protocol (SIP), Verto, Skinny Client Control Protocol (SCCP), H.323, Extensible Messaging and Presence Protocol (XMPP), GoogleTalk, T.38 and others.[22]

FreeSWITCH provides an application programming interface that exposes primitives for call control and IVR functionality. Applications may be written in the C language, C++, Python, Perl, Lua, JavaScript, Java and Microsoft .NET via Microsoft's CLR or via Mono.[23]

Call control applications can use the Event Socket, which is an Internet socket-based communications facility within FreeSWITCH providing a language independent interface. The Event Socket Library (ESL) and "ESL-wrappers" are available for Erlang, JavaScript, Lua, Perl, PHP, Python, and Ruby.

As of FreeSWITCH version 1.4, support exists for WebRTC.[24]

In FreeSWITCH 1.6 support was added for Video muxing and complete WebRTC, wss, dtls, SIP.js, Verto.js, Opus 48 kHz to 8 kHz, resilient up to 40% packet loss.

Main FreeSWITCH 1.6 features:

  • WebRTC support
  • Centralized User/Domain Directory (directory.xml)
  • Nanosecond CDR granularity
  • Call recording (In Stereo caller/callee left/right)
  • High Performance Multi-Threaded Core engine
  • Configuration via cURL to your HTTP server (mod_xml_curl).
  • XML Config files for easy parsing.
  • Protocol Agnostic
  • ZRTP support for transparent RTP based key exchange and encryption
  • Configurable RFC 2833 Payload type
  • Inband DTMF generation and detection.
  • Software based Conference (no hardware requirement)
  • Wideband Conferencing
  • Media / No Media modes
  • Proper ENUM/ISN dialing built in
  • Detailed CDR in XML
  • Radius CDR
  • Subscription server
  • Shared Line Appearances
  • Bridged Line Appearances
  • Enterprise/Carrier grade Eventing Engine. (XML Events, Name Value Events, Multicast Events)
  • Loadable File formats and streaming
  • Stream to and play from Shoutcast and Icecast
  • Multi-lingual Speech Phrase Interface
  • ASR/TTS support (native and via MRCP)
  • Basic IP/PBX features
  • Automated Attendant
  • Custom Ring Back Tones (Early Media)
  • XML-RPC support
  • Multiple format CDRs supported
  • SQL Engine provides session persistence
  • Thread Isolation
  • Parallel Hunting
  • Serial Hunting

WebRTC support[edit]


  • FreeSWITCH is a WebRTC Gateway, able to accept encrypted media from browsers, convert it, and exchange it with other communication networks, that use different codecs and encryptions, e.g.: PSTN, mobile carriers, legacy systems, etc. FreeSWITCH can be the gateway between SIP network and applications and browsers on desktops, tablets and smartphones.
  • FreeSWITCH is a WebRTC Application Server, able to directly provide native services to browsers, like videoconferences, IVRs, Call Centers, without the use of any gateway or third party. FreeSWITCH can directly provide services through Secure WebSocket (WSS), SRTP, and DTLS, the native WebRTC protocols.
  • FreeSWITCH makes available an additional Signaling Plane because with Verto the browsers can initiate or receive a voice call or a video call in the easiest way, and they can chat, share screen, receive and send data in real time to back end applications. Verto is an alternative to XMPP or SIP in Javascript. FreeSWITCH can serve in parallel and concurrently the same application to clients that use signaling in SIP and Verto.

Video conferencing support[edit]

[26] FreeSWITCH has always been a powerful platform for conferencing, starting many years ago as a hugely scalable audio conferencing bridge. In a breakthrough at ClueCon 2015 in Chicago Illinois, FreeSWITCH's creator Anthony Minessale II announced support for video transcoding, mixing, manipulation, and Multipoint Control Unit (MCU) functionality. FreeSWITCH now has the most advanced and mature video conferencing features:

  • Multiple video codecs support and transcoding
  • Multiple video layouts
  • Screen splits
  • Picture in picture
  • Screen sharing
  • Video superimposing (captions, logos, and so on)
  • Video mixing
  • Video effects and real-time manipulation
  • Chroma-Key (video mixing a background)
  • SIP, WebRTC, VERTO, ISDN participants

Codec support[edit]

FreeSWITCH supports a variety of audio and video codecs:[27]

G.723.1, H263 and H264 are supported in pass-through mode. Since the raw compressed data is passed through between callers without any processing, this allows support for some codecs that cannot be provided free of charge due to patent or other licensing issues.

The software supports hardware transcoding cards, such as produced by Sangoma.[29] These implement codecs in hardware, reducing the CPU usage of the server. Some of these codecs are fully licensed, providing an alternative to the pass-through options above.

Protocol support[edit]


  • SIP with mod_sofia
    • UDP, TCP, SCTP and TLS transports for full SIP compliance.
    • xiWS and WSS transports for full WebRTC compliance.
    • SIP v.2.0 (RFC 3261)
    • IPv6 Support
    • SIP Session timers
    • RTP Timers
    • RFC 3263 (SRV and NAPTR)
    • RFC 3325
    • RFC 4694
    • SRTP via SDES (Works with Polycom, Snom, Linksys and Grandstream)
    • Blind SIP Registration
    • STUN Support
    • Jitter buffer
    • NAT Support
    • Distributed SIP registrations
    • Late Codec Negotiation
    • Multiple SIP registrations per user account.
    • Multitenancy - Multiple SIP UAs
    • SIP Reinvites.
    • Can act as an SBC (Session Border Controller)
    • Manage Presence
    • SIP/SIMPLE (can gateway to other chat protocols)
    • SIP Multicast Paging support for Linksys and Snom
    • Intercom/AutoAnswer support.
    • Call features like Call Hold (Re-INVITE), Blind Transfer (REFER), Call Forward (302), etc.
  • mod_skinny - Skinny Call Control Protocol (SCCP)
  • mod_verto - VERTO WebRTC Signaling Protocol

Application support[edit]


  • Voicemail
    • Multitenancy - Enterprise/Carrier configuration
    • Time of Day Greetings
    • Urgent Message Tagging
    • E-mail Delivery
    • Playback and Rerecord messages before delivery.
    • Keys are templates so you can rearrange to fit your needs.
    • Callback support from inside voicemail.
    • Podcast of Voicemail (RSS)
    • Message Waiting Indicator (MWI)
  • Support for Queues (via mod_fifo or mod_callcenter)
  • Parking (via mod_fifo)
  • Conference
    • Software based Conferencing without any hardware requirements.
    • Wideband conferences.
    • Multiple on-demand or scheduled conferences with entry/exit announcements
    • Play files into the conference or a single member.
    • Relationships
    • TTS integration
    • Transfers
    • Outbound Calling
    • Configurable Key Lay
    • Volume, Gain and Energy level per call.
    • Bridge to Conference transition
    • Multi Party outbound dialing.
    • RFC 4579 SIP CC Conferencing for UAs
    • Automatic or on-demand recording
  • RSS Reader
  • Fax endpoint, gateway and passthrough mode.
    • T.30 (G.711) Audio Fax (via mod_spandsp) formerly known as mod_fax.
    • T.38 faxing (gateway, endpoint and passthrough)

Encryption support[edit]

Text-to-speech and Automatic Speech Recognition support[edit]

Operating and build system support[edit]

  • Debian Linux is the preferred operating system as it provides the broadest support in its libraries necessary to run FreeSWITCH unencumbered by licensing restrictions
  • Other Linux systems, such as RHEL and CentOS
  • Solaris 10 UNIX (Solaris Studio)
  • FreeBSD (gmake)
  • macOS (gmake)
  • Windows (native)

Comparison with other telephony software[edit]

FreeSWITCH occupies a space between pure switches that simply route calls, such as Kamailio and OpenSIPS, and those that provide primarily PBX or IVR functionality, such as Asterisk and its derivatives. FreeSWITCH provides building blocks from which applications – such as a PBX, a voicemail system, a conferencing system or a calling card – can be built using any of the supported languages.[32]

Derived products[edit]

FreeSWITCH is a core component in many PBX in a box commercial products and open-source projects. Some of the commercial products are hardware and software bundles, for which the manufacturer supports and releases the software as open source.

See also[edit]


freeswitch gui application

  1. ^ "Releases - signalwire/freeswitch". Retrieved 25 March 2021 – via GitHub.
  2. ^ "Linux - FreeSWITCH - Confluence".
  3. ^ "macOS - FreeSWITCH - Confluence".
  4. ^ "Solaris - FreeSWITCH - Confluence".
  5. ^ "FreeBSD - FreeSWITCH - Confluence".
  6. ^ "NetBSD - FreeSWITCH - Confluence".
  7. ^ "OpenBSD - FreeSWITCH - Confluence".
  8. ^ "DragonFlyBSD - FreeSWITCH - Confluence".
  9. ^ "Windows - FreeSWITCH - Confluence".
  10. ^ "Beyond Asterisk, The Future of Telephony. What's Next?". O'Reilly Media. 2006-01-25. Retrieved 2007-10-06.
  11. ^ "Truphone Selects FreeSWITCH and TelcoBridges to Enable VoIP Calls over WiFi on Mobile Phones" (Press release). Truphone. June 5, 2007.
  12. ^ "Gaboogie Embraces Open Source For New Mobile Group Calling and Conference Calling Solution". Gaboogie. 2007-08-03. Archived from the original on 2008-09-08. Retrieved 2007-10-06.
  13. ^ "FreeSWITCH 1.0.0 "Phoenix" Released!". Archived from the original on 2008-08-10.
  14. ^ "FreeSWITCH 1.0.1 "Phoenix" Released!". Archived from the original on 2008-08-19.
  15. ^ "ClueCon 2012 Keynote Address". Archived from the original on 2012-06-08.
  16. ^ "It's Official! FreeSWITCH 1.2 Has Been Released". Archived from the original on 2012-09-20.
  17. ^ "Freeswitch acquired by SignalWire". Retrieved 1 May 2018.
  18. ^ Gallagher, Kathleen (October 18, 2009). "Flipping the FreeSWITCH – Brookfield is home to revolutionary software". Milwaukee Journal Sentinel. Archived from the original on October 22, 2009.
  19. ^ "An Interview with the Creator of FreeSWITCH". O'Reilly Media. July 25, 2006.
  20. ^ A complete list of dependencies can be found in the dependencies page section of the FreeSWITCH documentation.
  21. ^ "FreeSWITCH Introduction". FreeSWITCH Wiki. Retrieved 29 January 2016.
  22. ^ "Modules". FreeSWITCH Documentation Wiki. 2016-01-29. Retrieved 2007-10-07.
  23. ^ "Client and Developer Interfaces". FreeSWITCH Documentation Wiki. 2016-01-29. Retrieved 2007-10-07.
  24. ^ "FreeSWITCH Project Releases Version 1.4 Beta with WebRTC Media Support". FreeSWITCH Official Website. 2013-06-19. Retrieved 2013-06-19.
  25. ^ FreeSWITCH 1.6 Cookbook, Packt Publishing, ISBN 1785280910
  26. ^ Mastering FreeSWITCH, Packt Publishing, ISBN 1784398888
  27. ^ "Audio Codecs - FreeSWITCH - Confluence".
  28. ^ "Archived copy". Archived from the original on 2010-11-23. Retrieved 2010-11-23.CS1 maint: archived copy as title (link)
  29. ^ Archived 2013-07-05 at the Wayback Machine
  30. ^ "Specifications - FreeSWITCH - Confluence".
  31. ^ "Specifications - FreeSWITCH - Confluence".
  32. ^ "FreeSWITCH Applications". Retrieved 30 January 2016.